In integrated optics/optoelectronics, one of the major problems is the achievement of a cost-effective and low-loss coupling between incoming/outgoing glass fibers and the dielectric waveguides or functional components, resp., on the chip. Because of the small core diameters of the waveguides and thus spot diameters of the guided light in the order of 10 .mu.m, high requirements exist with regard to alignment techniques between glass fibers and a chip, since tolerances in the order of .mu.m would already lead to substantial coupling losses of several dB.
Known in the art is the coupling through planar front faces where basically two different approaches are used:
In a first prior art approach, the alignment between fiber and chip can be performed actively, i.e. the fiber to be coupled is moved by micro-manipulation relative to the chip, with the light source being switched on, until a maximum over-coupling is detected. Then an attachment of the fiber at the chip is made. This approach guarantees minimum coupling losses. However, this approach is expensive, in particular with branching circuits.
The second approach uses passive alignment by means of a fiber guide structure integrated in the substrate of the chip, commonly a V-shaped groove. This groove can be produced in Si by anisotropic etching. The production of a high-grade planar front face at the end of the groove requires special approach steps, such as described, e.g., in DE 41 42 850 and DE 41 34 940. Alternatively, such a groove structure can also be produced in polymers by molding processes, the original mould being produced by a method as described, e.g., in DE 42 12 208.
While the second approach permits, in principle, a cost-effective manufacture of integrated optical components, it will result, however, in comparatively high and not repeatable coupling losses. This is due both because the fiber diameter is subjected to variations, and because the fiber core may be positioned eccentrically to the center axis. While the effects of diameter variations can be reduced by expensive counter-measures, it is by principle impossible to compensate the core eccentricity with passive alignment. Further problems are the manufacture of high-grade front faces at the end of the groove and the occurrence of back-scatter. This is unavoidable in the front-face coupling method in a not always tolerable degree. Such back-scatter is only reduceable by an expensive sloped grind.